M. I. Yanovskaya

Bio: M. I. Yanovskaya is an academic researcher from Moscow State University. The author has contributed to research in topic(s): Alkoxide & Barium titanate. The author has an hindex of 9, co-authored 23 publication(s) receiving 267 citation(s).

Hydrolysis of molybdenum and tungsten alkoxides: sols, powders and films

Abstract: Hydrolysis of molybdenum and tungsten alkoxides of the two series MO(OEt)4 and MO2(OEt)2 (M = Mo, W) has been studied. Hydrolysis products and the partially hydrolyzed solutions have been characterized by means of X-ray diffraction, IR, electron spectroscopy and small-angle X-ray scattering. Preparation of stable sols is reported and their structures are discussed in terms of a fractal model. While ‘tungsten solutions’ may be described as typical polymeric sols, ‘molybdenum solutions’ should be regarded as particulate sols. The reason for this difference has its origin in the structures of alkoxides and mechanisms of their hydrolysis. Sols were used for the preparation of electrochromic and photochromic films by spin-coating techniques. A coloration mechanism is discussed in terms of the percolation model. Some properties of the composite structures WO3TiO2, n-SiWO3 are also reported.

Physicochemical approach to the studies of metal alkoxides

Abstract: The review provides a description of main events in the development of chemistry of metal alkoxides in Russian and summarizes the results obtained by the authors. The studies of solubility and vapor pressure in the M(OR)n-ROH (R  Li, Mg, Ca, Sr, Ba, Tl) systems permitted the determination of the composition of the solvates formed and the optimization of the isolation conditions for distinct derivatives. The electrochemical synthetic approach to the alkoxide and 2-methoxyethoxide derivatives of III–VIII Group elements has been elaborated. Improvement of the MCln with NaOR metathesis conditions led to practically quantitative yields of alkoxides. The examples of the structures of polynuclear oxoalkoxides, earlier erroneously considered to be orthoderivatives, i.e. ‘M(OR)n’, are given. It has been stated that among the alkoxoderivatives of Zr and Hf these are only M(OC2H4OMe)4 and M(OR)4·ROH (RPri, Bui) that exist as individual compounds, while the samples of those with different R contain oxocomplexes of M3O(OR)10 and M4O(OR)14 composition. The questions connected with the origin of oxogroups in the molecules of alkoxides and their influence on the properties of the samples are discussed. The irreproducibility of the physicochemical constants for the samples (physical state, melting points, solubility in alcohols, intensity of coloration) is caused by different ‘chemical’ (synthetic procedures, isolation conditions) and the thermal prehistory and storage times; it originates from the difference in their molecular composition (different fractions of different types of oligomeric and polymeric [M(OR)n]m and MxOy(OR)z aggregates). Formation of bimetallic alkoxides is studied using the plotting to 20°C solubility isotherms in M(OR)n− M′(OR)m-Solvent systems. Different kinds of systems are considered and the composition and structure of bimetallic complexes and oxocomplexes, originating from their decomposition, are described. Decomposition of alkoxomolybdates and -tungstates in solution may result in crystallization of complex oxides as the final products. The example of MTiO3 (MMg, Ba) oxide preparation is discussed as most illustratively demonstrating the need in studies of metal alkoxides interaction in solution for the optimization of synthesis of oxides by the sol-gel technique.

Formation of LiNbO3 powders and thin films by hydrolysis of metal alkoxides

Abstract: Crystalline LiNbO3 was prepared by simultaneous hydrolysis of lithium and niobium alkoxides (in the mole ratio Li : Nb = 1 :1) followed by heat treatment. Crystallization of LiNbO3 occurs in a wide temperature region, 350 to 700° C, directly from an amorphous hydrolysis product containing residual alkoxy and hydroxy groups. Heat treatment at 700° C results in the formation of fully crystalline LiNbO3 powder with completely formed ferroelectric properties. Hydrolysis of metal alkoxide solutions is successfully used to obtain high-quality LiNbO3 crystalline thin films.

Synthesis and crystal structure of the double barium–titanium isopropoxide [Ba4Ti4(µ4-O)4(µ3-OR)2(µ-OR)8(OR)6(ROH)4][Ba4Ti4(µ4-O)4(µ3-OR)2(µ-OR)9(OR)5(ROH)3]

Abstract: An X-ray structural study of the crystals isolated from the solutions obtained by the reaction of Ba metal with Ti(OPri)4 in isopropyl alcohol has been carried out; the crystals of the compound, which is a precursor for the synthesis of BaTiO3, contain molecules of two different kinds [Ba4Ti4O4(OR)16(ROH)4] and [Ba4Ti4O4(OR)16(ROH)3], where R = Pri.

Application of metal alkoxides in the synthesis of oxides

Abstract: Powders and thin films of the following simple and complex oxides have been obtained from metal alkoxides: MIITiO3 (M= Mg, Ca-Ba), MM1/3B2/3O3 (M= Sr, Ba, M' = Mg-Zn; B= Nb, Ta); MNbO3(M= Li, Na); ZrTiO4; PbTiO3; PZT, PLZT-materials; M2BO4 (M= Li, Na; B= Mo, W), Bi2BO6(B= Mo, W); LixWO3, WO3, MoO3, Bi2O3-WO3(solid solutions), YFeO3, Y3Fe5O12; YBa2Cu3O7-; Bi2Sr2CaCu2Ox; Bi2Sr2Ca2Cu3Ox. For synthesis of metal alkoxides and solutions containing two or more elements electrochemical technique (the anodic dissolution of metals in alcohols) has been used. Analysis of different examples emphasises that considerable attention in sol-gel chemistry of oxides should be paid to decomposition of M(OR)n with elimination of ether and formation of oxoalkoxides, containing M-O-M' bonds-the basis of future oxide phases.

Aliphatic cyclic carbonates and spiroorthocarbonates as monomers

Abstract: In this review the synthesis and polymerization of aliphatic cyclic carbonates of different size and type are presented. The mechanisms of cationic, anionic, coordination and enzymatic polymerization of cyclic carbonates are discussed for obtaining polymers with well-defined structures and oligomers with reactive pendant and end groups. The reactions of cyclic carbonates with different nucleophilic reagents leading to products with CO2 retention or with decarboxylation are reported. Special attention has been paid to the synthesis and polymerization of spiroorthocarbonates, bicyclic acetals, which are the intermediates in the reaction of cyclic carbonates with cyclic ethers. The influence of the presence of neighboring groups such as methylene or epoxy groups on the polymerization mechanism of spiroorthocarbonates, as well as the volume expansion during polymerization is discussed. As a result of the above synthetic findings, a variety of novel materials have been developed with versatile applications in different fields such as biomedicine and electronics.

Photochromism of molybdenum oxide

Abstract: Molybdenum oxide can exhibit pronounced photochromism and thus might act as an excellent photonic material for a number of technical applications. In the early stage of the research, the attention was focused mainly on the (band) structure, photochromic mechanism and the behavior of the oxide. Later, many investigations were carried out on the factors that might influence the photochromic performance. At the same time, the photochromic response has been extended from UV light to visible light. In this review, the progress in all of these areas will be reviewed thoroughly.

The chemistry of methanol on the TiO2(110) surface: the influence of vacancies and coadsorbed species

Abstract: The chemistry of methanol was explored on the vacuum annealed TiO2(110) surface, with and without the presence of coadsorbed water and oxygen, using temperature programmed desorption (TPD), high resolution electron energy loss spectroscopy (HREELS), static secondary ion mass spectrometry (SSIMS) and low energy electron diffraction (LEED). The vacuum annealed TiO2(110) surface possessed about 8% oxygen vacancy sites, as determined with H2O TPD. Although evidence is presented for CH3OH dissociation to methoxy groups on the vacuum annealed TiO2(110) surface using SSIMS and HREELS, particularly at vacancy sites, the majority of the adlayer was molecularly adsorbed, evolving in TPD at 295 K. Although no evidence of irreversible decomposition was found in the TPD, dissociative CH3OH adsorption at 135 K on the vacuum annealed TiO2(110) surface led to recombinative desorption states at 350 and 480 K corresponding to methoxys adsorbed at non-vacancy and vacancy sites, respectively. Coadsorbed water had little or no influence on the chemistry of CH3OH on the vacuum annealed TiO2(110) surface, however new channels of chemistry were observed when CH3OH was adsorbed on the surface after O2 adsorption at various temperatures. In particular, O2 exposure at 300 K resulted in O adatoms (via dissociation at vacancies) that led to increased levels of CH3O–H bond cleavage. The higher surface coverage of methoxy then resulted in a disproportionation reaction to form CH3OH and H2CO above 600 K. In contrast, low temperature exposure of the vacuum annealed TiO2(110) surface to O2 resulted in low temperature state of O2 (presumably an O2- species) that oxidized CH3OH to H2CO by C–H bond cleavage. These results provide incentive to consider alternative thermal and photochemical oxidation mechanisms that involve the interaction of organics and oxygen at surface defect sites.

Sol–gel electrochromic coatings and devices: A review

Abstract: A brief updated review is made on sol-gel-derived electrochromic films (some of which used as ion storage films) of different chemical systems. Performances of selected films measured in electrochemical cells or in devices are discussed and the degradation problems experienced by different authors enumerated.